SARS-CoV-2, the novel coronavirus that causes COVID-19, emerged in China in late 2019 and rapidly reached pandemic status. The virus displays tropism for the respiratory system, causing symptoms that range from an acute respiratory syndrome, manifested in mild form in the vast majority of cases, and progressing in some cases to an extremely severe and rapidly developing type of pneumonia with major respiratory failure, evolving to death 11. World Health Organization. Coronavirus disease (COVID-19) pandemic. https://www.who.int/emergencies/diseases/novel-coronavirus-2019 (acessado em 14/Abr/2020).https://www.who.int/emergencies/diseases... .

However, it is possible that an important risk factor for COVID-19 has not been included thus far in the global guidelines for control of the pandemic, namely smoking.

Smokers are part of the risk group for COVID-19. One can infer the group’s increased risk of infection to the extent that smokers tend to hold smoking products to their mouths (whether conventional cigarettes or electronic smoking devices - ESDs) without adequate prior hand hygiene.

Another relevant factor is the risk of smokers suffering burns when lighting a cigarette or handling a waterpipe after hand hygiene with alcohol in gel, a highly flammable product.

As for the harms from COVID-19 infection, smoking increases the risk of lung damage. Smoking is related to bronchiolitis (generally asymptomatic), various types of pneumonia, chronic bronchitis, pulmonary emphysema, tuberculosis, and lung cancers, leading to decline in lung function 77. U.S. Department of Health and Human Services. The health consequences of smoking: 50 years of progress. A report of the Surgeon General. Atlanta: U.S. Department of Health and Human Services; 2014..

Despite the plausibility that these complications are due to the impacts of smoking, some studies have failed to report a relationship between smoking and progression of COVID-19.

The possible explanations for these conflicting findings may be found in the article by Szklo 1919. Szklo AS. Associação entre fumar e progressão para complicações respiratórias graves em pacientes com Covid-19. Rev Bras Cancerol 2020; 66:e-03974., including incorrect identification of smokers, economic vulnerability, heightened attention to exposure to the virus, and less presence due to tobacco-free environments laws. Additional factors could be the definition of smokers used in the studies (e.g., defining users of electronic cigarettes as non-smokers and time since last tobacco use) and information bias, considering that verbal communication is limited between health professionals, family members, and patients with more serious cases of COVID-19.

Thus, the alterations and lung damage caused by tobacco products and ESDs can be considered risk factors for the more severe manifestations and progression of COVID-19.

With the arrival of the COVID-19 pandemic, uncertainties concerning the future and social isolation measures are associated with preoccupation towards the disease. In this scenario, people may develop emotional responses that interfere negatively in their self-efficacy, since they feel emotionally vulnerable to face a real threat, being able to appeal to inappropriate strategies, such as smoking, in an attempt to reduce emotional imbalance 2424. Salvetti MG, Pimenta CAM. Dor crônica e a crença de auto-eficácia. Rev Esc Enferm USP 2007; 41:135-40..

Although there are no data on smoking and relapse during epidemics, studies have suggested that smokers exposed to natural disasters tend to smoke more than unexposed smokers 2525. Huh J, Timberlake DS. Do smokers of specialty and conventional cigarettes differ in their dependence on nicotine? Addict Behav 2009; 34:204-11. and that former smokers are more likely to relapse 2626. Lanctot JQ, Stockton MB, Mzayek F, Read M, McDevitt-Murphy M, Ward K. Effects of disasters on smoking and relapse: an exploratory study of Hurricane Katrina victims. Am J Health Educ 2008; 39:91-4..

During social isolation and stay-at-home orders, active smokers expose non-smokers to second-hand smoke. Secondhand smoke can cause smoking similar damage 2727. U.S. Department of Health and Human Services. The health consequences of involuntary exposure to tobacco smoke: a report of the Surgeon General. Atlanta: U.S. Department of Health and Human Services; 2006., including increased ACE-2 expression 88. Brake SJ, Barnsley K, Lu W, McAlinden KD, Eapen MS, Sohal SS. Smoking upregulates angiotensin-converting enzyme-2 receptor: a potential adhesion site for novel coronavirus SARS-CoV-2 (Covid-19). J Clin Med 2020; 9:E841.. One cannot rule out the emission of aerosols containing the virus, especially in ESDs, which operate at lower temperatures. More studies are necessary to determine the extent of impacts of secondhand smoke on COVID-19 transmission and progression.

Gas exchange, lung function, and blood circulation, processes directly affected in COVID-19, improve quickly after smoking cessation 1010. U.S. Department of Health and Human Services. Smoking cessation: a report of the Surgeon General. Atlanta: U.S. Department of Health and Human Services; 2020.. Quitting smoking and avoiding exposure to tobacco smoke and vapors can have a positive impact, reducing the risk involved in COVID-19 and smoking.

Acknowledgments

The authors wish to thank the Brazilian Health Regulatory Agency (Anvisa), the Oswaldo Cruz Foundation (Fiocruz), the Heart Institute, Clinical Hospital, School of Medicine, University of São Paulo (InCor/HC/FMUSP), and the Brazilian National Research Council (CNPq). The article expresses the sole opinions and ideas of the authors based on the currently available scientific evidence and does not represent any guidelines or institutional opinions on the part of Anvisa, InCor/HC/FMUSP, Fiocruz, the Brazilian Ministry of Health, or the Brazilian government.

U.S. Department of Health and Human Services. The health consequences of involuntary exposure to tobacco smoke: a report of the Surgeon General. Atlanta: U.S. Department of Health and Human Services; 2006.